Combustion engines such as diesel engines, gasoline engines, and gaseous fuel-powered engines are supplied with a mixture of air and fuel for combustion within the engine that generates a mechanical power output. In order to increase the power output generated by this combustion process, the engine is often equipped with a turbocharger. The turbocharger, driven by exhaust energy from the engine, forces more fresh air into combustion chambers of the engine than would otherwise be possible. This increased amount of fresh air allows for enhanced fueling that further increases the power output of the engine. Unfortunately, in some situations (e.g., during transition between low and high loads at low engine speed or during continuous operation at low speed or load), the amount of exhaust energy available to drive the turbocharger may be insufficient for the turbocharger to quickly provide a desired amount of fresh air. In these situations, a capacity, an efficiency, and/or emissions of the engine can be negatively impacted.
In addition to the goal of increasing engine power output and efficiency, it is often desirable to simultaneously reduce exhaust emissions. That is, combustion engines exhaust a complex mixture of air pollutants as byproducts of the combustion process and, due to increased attention on the environment, exhaust emission standards have become more stringent. The amount of pollutants emitted to the atmosphere from an engine can be regulated depending on the type of engine, size of engine, and/or class of engine.
One method implemented by engine manufacturers to comply with the regulation of pollutants exhausted to the environment has been to trap, reduce, convert, or otherwise remove gaseous compounds and solid particulate matter from the exhaust flow of an engine with filters and/or catalysts. These filters and catalysts, however, may only function efficiently under particular operating conditions. For example, some filters only function for a period of time, until they become saturated with particulate matter. In order for the filters to continue operation, they may need to be heated above a combustion threshold of the trapped matter such that the pollutants are burned away. Similarly, catalysts may only function efficiently when exposed to elevated temperatures.
An attempt to address one or more of the problems described above is disclosed in U.S. Pat. No. 7,028,648 issued to Hasegawa et al. on Apr. 18, 2006 (the '648 patent). In particular, the '648 patent discloses a multi-cylinder engine having a plurality of cylinders sharing a single crankshaft. The combustion characteristics in the respective cylinders are improved by taking out some of the combustion gas produced within one of the cylinders at an early stage of an expansion stroke, and then introducing the combustion gas into another of the cylinders during a suction or compression stroke. This gas sharing between cylinders is accomplished by way of a dedicated cylinder-to-cylinder conduit and associated valves.
Although the system of the '648 patent may help to improve combustion characteristics within an engine, it may still be less than optimal. In particular the system of the '648 patent may still suffer turbocharger inefficiencies during transitional situations and/or conditions that result in poor performance of exhaust treatment devices.
The disclosed engine system is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.